Solar cells can be a viable energy source by utilizing their ability to convert sunlight to electrical energy. Silicon is a semiconductor material used in the manufacture of solar cells; however, a limitation of silicon use relates to the cost of purifying it to solar grade (SG).
Several techniques used to purify silicon for solar cells are known. Most of these techniques operate on the principle that while silicon is solidifying from a molten solution, undesirable impurities can tend to remain in the molten solution. For example, the float zone technique can be used to make monocrystalline ingots, and uses a moving liquid zone in a solid material, moving impurities to edges of the material. In another example, the Czochralski technique can be used to make monocrystalline ingots, and uses a seed crystal that is slowly pulled out of a solution, allowing the formation of a monocrystalline column of silicon while leaving impurities in the solution. In yet another example, the Bridgeman or heat exchanger techniques can be used to make multicrystalline ingots, and use a temperature gradient to cause directional solidification.